Purification and hydrogenation of furan concentrates

ABSTRACT

Furan concentrates containing deleterious unsaturated contaminants including sulfur compounds are purified prior to hydrogenation by contacting with zinc oxide either prior to or subsequent to separation of high boiling materials from the concentrate with the result that the furan concentrate is hydrogenated to high purity product comprising either furan and saturated materials or tetrahydrofuran and saturated materials with extended hydrogenation catalyst life. In a preferred embodiment, the furan concentrate is obtained as the by-product stream from hydrocarbon oxidative dehydrogenation processes and is subjected to distillation to remove therefrom materials boiling above about 80*C prior to contacting with zinc oxide and hydrogenation.

United States Patent [1 1 Johnson et a].

[ PURIFICATION AND HYDROGENATION OF FURAN CONCENTRATES [75] Inventors: Marvin M. Johnson; Donald C.

Tahler, both of Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

22 Filed: Sept. 6, 1972 [2i 1 Appl. No; 286,728

Related US. Application Data [63] Continuation-in-part of Ser. No. 175,432. Aug. 27,

1971, abandoned.

OTHER PUBLICATIONS House, Modern Synthetic Reactions, N.Y., W. A. Benjamin (1965), p. 14.

[4 1 May 13, 1975 Primary Examinerl lenry R. Jiles Assistant Examiner-Bernard l. Dentz [57] ABSTRACT Furan concentrates containing deleterious unsaturated contaminants including sulfur compounds are purified prior to hydrogenation by contacting with zinc oxide either prior to or subsequent to separation of high boiling materials from the concentrate with the result that the furan concentrate is hydrogenated to high purity product comprising either furan and saturated materials or tetrahydrofuran and saturated materials with extended hydrogenation catalyst life. In a preferred embodiment, the furan concentrate is obtained as the by-product stream from hydrocarbon oxidative dehydrogenation processes and is subjected to distillation to remove therefrom materials boiling above about 80C prior to contacting with zinc oxide and hydrogenation.

9 Claims, I Drawing Figure PURIFICATION AND HYDROGENATION OF FURAN CONCENTRATES This is a continuation-in-part application of our copending application having Ser. No. 175,432, filed Aug. 27, I971 now abandoned, entitled Purification and Hydrogenation of Furan Concentrates."

This invention relates to the purification and hydrogenation of streams containing furan. In accordance with another aspect, this invention relates to the purification and hydrogenation of a furan concentrate obtained as part of an effluent from an oxidative dehydrogenation process. In accordance with another aspect, this invention relates to rendering deleterious contami nants including sulfur compounds present in furan concentrates innocuous by contacting with zinc oxide prior to hydrogenation of the furan. In accordance with a further aspect, this invention relates to the purification of furan concentrates containing catalyst inactivating materials by separating therefrom materials boiling above about 80C either prior to or subsequent to Zinc oxide contacting of the furan concentrate, prior to hydrogenation. In accordance with another aspect, this invention relates to the oxidative dehydrogenation of hydrocarbons followed by the recovery of a furan concentrate from the effluent which concentrate is purified prior to hydrogenation to tetrahydrofuran by a combination of distillation and zinc oxide treatment. In accordance with a further aspect, it has been found that unsaturated materials such as olefins, acetylenes, and diolefins can be selectively hydrogenated in the presence of unsaturated ethers. In accordance with still another aspect, this invention relates to a process for hydrogenating furan concentrates to high purity products comprising either furan and saturated materials or tetrahydrofuran and saturated materials.

In a recent butene dehydrogenation process known as oxidative dehydrogenation, an oxygen-containing gas is fed to the catalytic reaction zone containing a catalyst such as stannic phosphate along with the butene feed and steam, and a substantial portion of the hydrogen produced by dehydrogenation is combusted to water vapor. This not only removes the inhibiting effect of the hydrogen on further dehydrogenation, but also supplies heat to this endothermic reaction resulting in high conversions and per-pass yield of butadiene at relatively good selectivity. By this method, additional steam is produced which is recovered from the process effluent as condensate. Also, moderate concentrations of oxygenated hydrocarbons are generated which similarly appear in the condensed steam and/or in the hydrocarbon effluent.

A highly reactive dehydrogenation catalyst comprising tin phosphate has recently been disclosed and claimed by Nolan in U.S. Pat. No. 3,320,329. As is set forth in that patent, compounds to be dehydrogenated, preferably selected from the group consisting of alkenes, cycloalkenes, alkylpyridines, and alkyl aromatics, are mixed with oxygen or an oxygen-containing gas, preheated, and passed over a catalyst comprising stannic phosphate at a temperature in the range of 700 to I300F. Generally, the inlet temperature of the gas is around 800 to 900F.

The oxygen used in the dehydrogenation is present in an excess in order to insure complete conversion of hydrogen released in the dehydrogenation reaction. Therefore, the effluent from the dehydrogenation reaction will contain unreacted oxygen gas as well as a numher of oxygenated products of the reaction. This residual oxygen and the oxygenated compounds are corrosive and are subject to polymerization and are, therefore, detrimental to the further processing of the hydrocarbon product. It is, therefore, necessary that the oxygen and oxygen-containing compounds be removed from the effluent streams.

It has been found that a small percentage of the olefin feed is converted to oxygenated hydrocarbons such as furans, alcohols, acids, aldehydes, ketones, etc., the nature and quantity of these compounds depending upon the conditions under which the dehydrogenation is effected. Under normal plant operating conditions, these oxygenated by-products will be ultimately fed into the atmosphere and/or discharged with waste water and/or end up in a heavy hydrocarbon-containing fraction, depending upon the separation and recovery processes employed and their operating conditions.

The present invention is directed to the purification of furan concentrates containing catalyst inactivating materials and subsequently hydrogenating the purified furan concentrate to produce high purity products comprising either furan and saturated materials or tetrahydrofuran and saturated materials.

It has been found that not all furan concentrates can be hydrogenated with equal ease and that in some instances the life of the hydrogenation catalyst is relatively short. Since hydrogenation catalysts are ordinarily quite expensive, e.g., nickel catalysts, and ordinarily not readily regenerable, short catalyst life is an important economic consideration in the production of tetrahydrofuran.

It has now been found that the cause of the problem is the somewhat unexpected presence of sulfur compounds in the furan concentrates. The source of the sulfur compound contamination is not known with certainty, but it is presently surmised that the water, of which copious quantities are used in the oxidative dehydrogenation process, is possibly the source because of the sulfite 0r sulfate compounds it may contain either naturally or from prior water treatment processes.

Irrespective of where the sulfur comes from, we have identified the problem and have now provided an effective and novel solution to the problem of poor or erratic hydrogenation of furan concentrate.

In accordance with the invention, it has now been found that the nature of the furan concentrate is such that it requires, to be readily hydrogenatable, both a separation to a selected end point and a high temperature treatment in contact with zinc oxide.

Accordingly, an object of this invention is to provide an improved process for the hydrogenation of furan concentrate.

Another object of this invention is to provide a process for the removal of deleterious contaminants including sulfur compounds from furan concentrates prior to hydrogenation.

A further object of this invention is to provide a process for the purification of furan concentrates to improve the hydrogenatability of the concentrates.

Other objects and aspects, as well as the several advantages of the invention, will be apparent to those skilled in the art upon reading the specification, the drawing, and the appended claims.

In accordance with the invention, the hydrogenatability of furan concentrates containing deleterious con taminants including sulfur compounds is improved by subjecting the concentrate to a high temperature treatment in contact with zinc oxide.

In accordance with one embodiment of the invention. a furan concentrate is separated into a high boiling and a low boiling fraction, and the low boiling frac tion contacted with zinc oxide prior to hydrogenation to convert furan to tetrahydrofuran.

In accordance with another embodiment of the invention, it has been found that unsaturated materials such as acetylenes, olefins and diolefins can be selectively hydrogenated to saturated materials in the presence of unsaturated ethers such as furan by contacting with selected catalysts under hydrogenation conditions.

In accordance with another embodiment of the invention. furan concentrates containing unsaturated materials such as olefins, acetylenes and diolefins, as well as sulfur compounds, are hydrogenated to high pu rity products comprising either furan and saturated materials or tetrahydrofuran and saturated materials, the hydrogenation being carried out in the presence of lected hydrogenation catalysts under hydrogenation conditions.

In accordance with carrying out the hydrogenation using a catalyst and reaction conditions which are milder and more selective to selectively hydrogenate unsaturated materials in the presence of furan. for example, the furan concentrate is selectively hydrogenated such that the more readily hydrogenatable olefins, diolefins, alkynes, and the like are hydrogenated, but the furan is affected but little if at all. A product of this hydrogenation thus would be a furan concentrate in which the furan is diluted with hydrocarbons which are essentially paraffmic. Although the paraffin-diluted furan mixture is not readily separable by fractionation, there are applications where this furan mixture can be used without prior removal of the paraffins such as being used for a polymerization feed.

ln accordance with a specific embodiment, furan concentrates containing hydrogenation catalyst inactivating materials are purified prior to hydrogenation by subjecting the furan concentrate first to distillation to remove therefrom materials boiling above about 80C, followed by contacting at high temperature with Zinc oxide.

Further in accordance with the invention, the effectiveness of the zinc oxide absorbent used in desulfuriz ing the furan concentrate prior to hydrogenating furan concentrate is improved and the capacity of the bed to hold the sulfur is increased by impregnating the zinc oxide with a base, for example, an inorganic base such as sodium hydroxide, sodium carbonate, sodium zincate, and the like.

In accordance with another embodiment of the invention, the furan concentrate is first contacted at high temperature with zinc oxide and then subjected to distillation to remove therefrom materials boiling above about 80C prior to hydrogenation of the concentrate.

In accordance with a further specific embodiment of the invention, a furan concentrate is obtained as a portion of the effluent from a butenes oxidative dehydrogenation. which concentrate is subjected to distillation to a selected end point and a high temperature treatment in contact with zinc oxide prior to hydrogenation.

The furan concentrate, hereinafter called the first furan concentrate. which is applicable for the treating and hydrogenation sequence of the present invention is a substantially water-insoluble furan-containing fraction of the by-products formed from an oxidative dehydrogenation process wherein a hydrocarbon is converted to at least one less saturated product. The specific hydrocarbon feed or the specific catalyst of the oxidative dehydrogenation is not critical. Preferably, however, the feed is a C hydrocarbon, particularly normal butenes. The oxidative dehydrogenation of butenes to butadiene can be carried out in the presence of a number of catalysts including a tin phosphate catalyst as disclosed and claimed by Nolan in U.S. Pat. No. 3,3 20,3 29, as well as in the presence of other catalysts such as calcined catalytic composition prepared from a phosphorus-containing material, such as phosphoric acid. a tin material such as tin chloride, and one of a Group IA or "A metal or metal-containing material disclosed and claimed in copending application of Nolen et a], Ser. No. 175.398, filed Aug. 26, 1971. The by-product furan fraction can be narrow or broad in boiling range, but should contain a significant amount of furan, say, at least 5 weight percent. Preferably, it should be relatively free of lighter boiling material such as butenes and butadiene, but this is an economic rather than a technical preference.

In practice. the first furan concentrate can be obtained by consecutively subjecting the oxidative dehydrogenation reactor effluent to remove of water and water-solubles such as by an aqueous quenching step, removal of light gases such as by an absorptionstripping step, and removal of principal dehydrogenation products by a fractionation step. The remaining furan-containing fraction is then subjected to the process combination of the present invention.

Because the furan concentrate is a broad boiling range material and apparently contains some heavier sulfuncontaining materials which do not readily respond to the zinc oxide treatment, it is necessary that the first furan concentrate be distilled to provide a second concentrate such that the end point of the second concentrate is less than the boiling point of thiophene, that is, less than about 84C (183.2F) at 760 mm Hg. Preferably, the end point of the distillate should be no more than about C l76.0F). Thus. the distillation should be carried out so as to provide a furancontaining distillate which is significantly free of materials boiling above about 80C (176F).

The boiling point of furan is about 32C (89.6F). However, because the complex mixture of the furan concentrates is capable of producing azeotropic mixtures, the effective boiling point of mixtures containing substantial amounts of furan can be as low as 28C (82.4F], or even lower. The presence of materials boiling below furan is not critical. Hence, this second furan concentrate can have any convenient initial boiling point (IBP).

In batch distillations, the second concentrate will generally contain a substantial amount of material boiling within the range of 28C (82.4F) to 80C (176F), preferably 28C (82.4F) to 60C (F), still more preferably 28C (82.4F) to 50C (122F). ln continuous operations, a continuously operating fractionating column will have its head temperature within one of these aforesaid ranges to produce a suitable second concentrate.

The zinc oxide treatment of the present invention comprises contact of the suitable furan concentrate with zinc oxide at temperatures in the range of from about 550 to about 850F and at any convenient pres sure such as. for example. atmospheric to about 250 psig. The contact is carried out in the vapor phase and at rates which will vary with the nature of the specific furan concentrate being treated. Ordinarily the rates will be in the range of from about 0.1 to about 10. preferably 1-5. IHSV. In general, the treatment will be sufficient to substantially reduce the total sulfur content of the furan concentrate.

Optionally. hydrogen can be present in the zinc oxide treatment zone in amounts ranging from trace amounts to those concentrations utilized in the subsequent furan hydrogenation stage.

The zinc oxide contactor ordinarily uses any suitable zinc oxide. either natural or synthetic, having a zinc oxide content greater than about weight percent, and preferably greater than about 50 weight percent. with the remainder being an inert binder such as a silicon-containing material. Other inert materials can be employed. If desired. Any convenient mode of contacting can be used although fixed bed operation is presently preferred.

As indicated above. the effectiveness of the zinc oxide absorbent can be improved by treatment of the zinc oxide with a base such as sodium hydroxide. sodium carbonate, sodium zincate. and the like prior to contacting with the furan concentrate. The amount of base added can be in the range of l to 10 weight percent. Other basic materials that can be employed include alkaline earth hydroxides such as calcium hydroxide and the other alkali metal carbonates, hydroxides and zincates such as the potassium derivatives.

Although the desulfurized second furan concentrate which is to be hydrogenated can be prepared for efficient hydrogenation by first undergoing the zinc oxide treatment and then the distillation. the reserve order of these treatments is presently preferred. That is. it is generally more convenient to subject the furan concentrate to the required distillation and then to carry out the zinc oxide treatment on the distillate. In has been found that the broad mixture of materials which comprise the furan concentrate contains at least minor amounts of readily polymerizable materials such as styrene. Hence. it is generally more convenient to first carry out the distillation because this operation separates the heavier styrene from the lighter fraction which contains the bulk of the furan. Operation in this manner minimizes the opportunity for polymerizables such as styrene to form polymers within the zinc oxide treater.

In accordance with one embodiment of the invention. the pretreated concentrate is hydrogenated using any suitable process and catalyst which is capable of converting the furan to maximum amounts of tetrahydrofuran with minimum amounts of n-butanol byproduct. Nickel-containing catalysts. such as Raney nickel, are particularly useful. Hydrogenation conditions can include l0()400F in temperature and 0l000 psig.

In accordance with another embodiment of the invention. if hydrogenation of the furan concentrate to an improved furan concentrate is desired. selective hydrogenation catalyst and conditions are used which are sufficient to convert olefins. diolefins. alkynes. and the like to the corresponding paraffins but are insufficient to convert significant amounts of the furan to tetrahydrofuran. Any catalyst system which has this desired degree of selectivity and any reaction conditions which have the desired degree of severity can be used to carry out this selective hydrogenation. A particularly appropriated group of catalysts can be represented by the empirical formula MeAs wherein Me represents nickel. cobalt. or iron. and x is a number which corresponds to the amount of arsenic required to sufficiently modify the metal catalyst to provide desired degree of selectivity. Nickel is preferred and x is preferably in the range of 0. l-O.5.

The metal arsenide is preferably supported on a conventional catalytic support material such as alumina. magnesia, charcoal. calcium aluminate. and the like. The support-containing catalyst will contain from about 0.1 to about 20. preferably 2l5. weight percent of the Me metal.

Such catalysts can be prepared by any suitable method. Conventional methods such as coprecipitation. impregnation. dry-mixing, wet-mixing. and com binations thereof can be used. impregnation methods are presently preferred and the suitable support material can be conventionally impregnated with inorganic compounds including salts such as the nitrates. halides. and the like of the metal components. Similarly. aqueous arsenic acid. or arsenic trioxide in an ammoniacal solution can be employed as impregnates.

Whichever method of catalyst preparation is used. the catalyst composite should be washed free of nonvolatiles. dried, then calcined at elevated temperatures in air. Finally. the catalyst is reduced with hydrogen at any suitable temperature and for any suitable time which is sufficient to produce the active catalyst. For example. the hydrogen reduction can be carried out at 5U0l [00F for O.l20 hours. In some instances. the calcination in air step can be omitted. Catalyst regeneration, when this is necessary. can follow a similar sequence of calcination and reduction.

When it is desired to produce a paraffin-diluted furan concentrate. the furan-containing material is brought into contact with a suitable catalyst together with hydrogen at temperatures in the range of about -750F, preferably l50-S00F. Any convenient pressure can be used such as from O to about 1000 psig. The process is preferably carried out continuously and at temperatures and feed rates which are sufficient to provide the level of hydrogenation severity to bring about the desired result. Feed rates will generally be in the range of 0.ll0 LHSV. The hydrogen will be present in the reaction zone to provide a molar ratio of hydrogen to feed of from about O.l:l to about 511.

A better understanding of the invention will be ob tained upon reference to the accompanying drawing which illustrates one embodiment of the invention in combinatiton with the processing following butenes oxidative dehydrogenation.

Referring now to the drawing. air by line H. hydrocarbon feed by line 12 and steam by line 13 are introduced into oxidative dehydrogenation (OXD) reactor 14. The conditions for carrying out oxidative dehydrogenation are set forth above and are described in detail in US. Pat. No. 3.320.329.

An oxidative dehydrogenation effluent. for example. a butenes oxidative dehydrogenation effluent comprising butenes. butadiene. isoprene. butyne-2. piperylenes, pentenes. etc., and oxygenated hydrocarbons including furan. steam, oxygen. and other materials, is removed from oxidative dehydrogenation reactor [4 by way of line 15, passed through cooler 16 wherein the effluent is cooled from the reactor temperature to the order of about 240F before passage to separate zone 17. It should be understood that a number of coolers can be provided to cool the oxidative dehydrogenation effluent to a suitable temperature for processing in sep aration zone 17. An aqueous phase. heavier hydrocar bons, and hea ier oxygenated hydrocarbons contained in the reactor effluent are removed from separation zone 17 by way of line 18. Unreacted hydrocarbons, dehydrogenated hydrocarbon product, eg, butadicne, and lighter materials contained in the effluent removed from reactor 14 are taken overhead from separation zone l7 by way ofline l9. Separation zone 17 can comprise a number of fractionators or a combination of fractionators and absorber-stripper unitsv A first furan concentrate is removed from separation zone 17 by way of line 20 and passed to distillation zone 21 wherein the concentrate is subjected to distillation conditions so as to remove as bottoms materials. including some sulfur compounds as thiophene, in the concentrate boiling above about 80 by way C. The heavier materials are removed from distillation zone way of line 22 to provide a second furan concentrate as an overhead distillate in line 23. This second furan concentrate in line 23 can be mixed with hydrogen if desired. by line 24, heated (not shown) and passed through treatment zone 25 containing zinc oxide. The feed to treating zone 25 is a mixture offuran and a number of close boiling olefins,diolefins, parafins, alkynes, and still contains catalyst-inactivating materials which are rendered innocuous by contact with zinc oxide in zone 25.

The second furan concentrate, now substantially freed of catalyst inactivating materials, is removed from zone 25 by way of line 26, cooled (not shown), mixed with additional hydrogen, ifnecessary, by way of line 27, and introduced into hydrogenation zone 28 wherein the furan is substantially converted to tetrahydrofuran (THF) depending upon the hydrogenation conditions and catalyst as disclosed above. lf desired, the hydrogenation conditions and catalyst can be so chosen as to hydrogenate substantially only the olefinic, acetylenic and diolefinic materials without hydro genating the furan, and the effluent produced would comprise furan and saturated hydrocarbon materials. The effluent is removed from hydrogenation zone by way of line 29, cooled (not shown), and passed to separation zone 30 wherein light materials are taken overhead by way of line 31 and heavier materials by way of line 32. Separation zone 30 can comprise two or more fractionators or other separation means. In one embodiment, a high purity tetrahydrofuran product is now removed by way of line 33 because its boiling point, about l5lF. is now substantially different from other members of the mixture. In another embodiment, a furan concentrate comprising furan and saturated hydrocarbon materials is removed as a high purity product and can be used as such without prior removal of the paraffinic hydrocarbons as a polymerization feedv The hydrogen introduced by either line 24 or line 27 can be added in the form of pure hydrogen, a hydrogen gas diluted with an inert diluent such as nitrogen, or any other hydrogen-containing gas. Reaction of hydrogen with the oxygen-containing materials and espe- 6 1000 psig, preferably about lUO to about 300 psig. The temperature, of course. depends on the type of catalyst employed. [f it is desired to produce a paraffin-diluted furan concentrate. the furan-containing material is brought into contact with a metal arsenide catalyst, as defined above, with hydrogen under suitable hydrogenation conditions. as defined above.

The hydrogenation of furan to tetrahydrofuran can be conducted with metal catalysts such as cobalt, nickel, and ruthenium with suitable supporting or diluting materials such as alumina, carbon, silica, or other similar materials. As indicated previously, the hydrogenation of unsaturated hydrocarbon materials present in the furan concentrate without any substantial amount of hydrogenation of the furan can be carried out in the presence of metal arsenide catalysts as defined above.

Although not shown in the drawing, the hydrogenation effluent which comprises principally hydrogen, tetrahydrofuran and paraffinic hydrocarbons such as butane and isopentane is removed from hydrogenation zone 28 and can be cooled by an exchanger (not shown and passed to a phase separator (not shown) prior to passing the effluent to other separation units of separation zone 30. uncondensed materials, including hydrogen removed from the hydrogenation effluent, are separated in the phase separator and can be returned to the hydrogenation reactor as recycle (not shown). Product liquid which comprises tetrahydrofuran, isopentane and butane and a small amount of hydrogen and other materials can be passed in toto to other separation units of separation units of separation zone 30 or a portion ofit can be recycled as feed to the hydrogena' t on zone for temperature control. In another embodiment, the hydrogenation effluent comprising hydrogen, furan and paraffmic hydrocarbons can be subjected to further separation or treatment as desired in a manner similar to that defined above for the recovery of tetrahydrofuran product,

EXAMPLE I Weight Component Percent Furan 49.62 Methacrolcin 8.66 Vinylcyclohexene 5.7) Benzene 5,96 Toluene 2.05 Others 7.92

Total Sulfur 190 ppm The abovedescribed first furan concentrate was passed through a cylindrical reactor which was packed with about ml of-l0/+4() mesh zinc oxide at a rate of about 4 LHSV. The reactor was maintained at 9 570-590F and 120 psig. The reactor effluent was found to contain 59 ppm total sulfur.

About 300 cc of the above ZnO-treated furan concentrate was then charged into an autoclave together with about 1 gram of Raney nickel catalyst for hydrogenation at 270F and at 500 psig. The hydrogenation was found to proceed very slowly. Consequently. the liquid was removed from the autoclave and distilled to a temperature of 37C (98.6%) and the overhead distillate in a manner similar to that of Example I the distilled second furan concentrate was passed over zinc oxide at 550? and at 200 psig. The effluent from the zinc oxide reactor was found to contain only l ppm total sulfur.

Also in a manner similar to that of Example the above distilled and zinc oxide-treated material was subjected to hydrogenation in the presence of Rabet Raney at 250F and at 500 psig. The hydrogenation to tetrahydrofuran was very rapid and was essentially was collected. The overhead distillate (l cc) was 10 complete i bn 2 hour The n is also found in found to have 3 ppm total sulfur. (about 10 cc liquid was lost in the operation.)

Table I as Run 5.

TABLE I Hydrogenation of Furan Concentrate Sulfur Content of Catalyst Hydrogenation Run Pro-Treatment of Pro-Treated Loading Temp. Rate No. Furan Concentrate Concentrate (Wtfk Feed) "F PSl/Min/g Ni 1 Distilled. overhead from IBP to 37%. (98.6%] I93 ppm 0.5 260 2 5 2 Distilled. overhead from 18F to 37C (98.6%) I93 ppm 5 270 I7 3 ZnO-treutcd but not distilled 59 ppm 0.5 270 V. Slow 4 ZnO-trcutcd. thcn distilled,

from 18F to 37C (98.6%) 3 ppm 0.5 260 70 5 Distilled, overhead from 8L5 to 84F, thcn ZnO-treatcd l ppm 0.5 250 I40 About 70 ml of the above distillate was diluted with 440 ml of n-pentane and mixed with Raney nickel. then subjected to hydrogenation at 500 psig at 260F. The uptake of hydrogen was found to be very rapid. and. after about 7 hours, it was found that the furan had been completely converted to tetrahydrofuran except for traces of n-butyl alcohol.

The results of this run are shown in Table l as Run No. 4. For purposes of comparison, the results of several other runs which utilized only the distillation or which utilized only the zinc oxide treatment are also shown. These are Runs 1, 2 and 3.

The data in Table I clearly shown the benefits obtained when the furan concentrate. containing a relatively large quantity of sulfur compounds, is subjected to both a zinc oxide treatment and a distillation to remove high boiling materials. in those runs in which only the distillation was employed or which only the zinc oxide treatment was employed, the hydrogenation rate was found to be very slow. Hydrogenation (not shown in the table) of the furan concentrate which is neither distilled nor subject to the zinc oxide treatment is even poorer than Runs 13.

EXAMPLE ii in this example of an invention run a different first furan concentrate, having a different level of sulfur compound contamination, was subjected first to a distillation and then to a zinc oxide treatment to render it easily hydrogenatable to tetrahydrofuran.

The first furan concentrate used in this run was similar to that described in Example I except that its total sulfur content was about 57 ppm. This concentrate was first distilled and an overhead fraction boiling at 8l.S-84F was collected. This fraction was found to contain about 23 ppm total sulfur and had an analysis, in weight percent, as shown below.

lsopcntanc 4.44 1.3-Pcntadicncs l.77 Furan 88.04 Othcrs 3.53 Butync-I ll? EXAMPLE iii A nickel arsenide/alumina catalyst was prepared by impregnating 86.4 g ofa l0-40 mesh granular catalytic grade gamma-alumina with an impregnating solution prepared by dissolving 42.6 g of Ni(No3) .6H- O, and g of H AsO in ml water. Essentially all the impregnating liquid was soaked by the alumina in three soaking operations with drying of the catalyst between the soakings. The impregnated alumina was then calcined at 900F in a stream of air for 3 hours. It was then heated in a flow of hydrogen at l000F for 5 hours. then cooled to room temperature in flowing hydrogen.

The resulting catalyst was found to contain 8.9 weight percent nickel and 4.6 weight percent arsenic. Thus, the empirical formula of the nickel arsenide on the alumina can be represented as NiAs EXAMPLE IV mole ratio of 0.63-0.84. The results of the hydrogena tion are shown in Table II below.

TABLE II Hydrogenation of Olcfins and Diolcfins in Furan Concentrate Hydrogenation Hytlrotrcatcd Component Feedstock Product n-Butane ND" 058 i-Pcntane ND (Hi8 n-Pentanc ND L23 trans-Pentene-Z 0.44 0.02 cis-Pentene-Z 083 ND 2 Methylbutene-2 0.24 0. l4

ND not LlLlccl 'A small amount of cyclopcntiidicnc hciiuctl present although the analytical method used could not tlctccl it The data in Table ll above shown that an improved furan concentrate, which is essentially free of olefinic. acetylenic. and diolefinic contaminants. can be prepared by using a selective hydrogenation catalyst. With minimal losses of furan to tetrahydrofuran and n-butyl alcohol, unsaturates such as cis-pentene-2, isoprene lbutyne. trans'pentadiene, cis-pentadiene, and cyclopentadiene were destroyed. Other olefins were substantially reduced.

EXAMPLE V Runs were carried out using zinc oxide with and without treatment with a base to treat a sulfur-containing furan concentrate prior to hydrogenation. In one run. zinc oxide was impregnated with about 7 weight percent sodium hydroxide prior to contacting with the furan concentrate The results of the runs. with and without sodium hy droxide treatment of a commercial zinc oxide absorbent. are given below in Table lll. It will be noted that it was possible to operate at twice the space velocity with the based treated Zinc oxide and still improve ab sorbent capacity.

TABLE Ill Run l Run 2 Absorbent Zinc oxide Zinc oxide Treatment (base) none 7% NaOH Process conditions:

1r. psig 200 200 Temperature. "F 540 560 WHSV 1.2 2.4 Capacity-Sulfur Content of Bed 1.7 to 2.2% S 34% S It will be observed from the above runs that the effectiveness of the zinc oxide absorbent used in desulfurizing the furan concentrate prior to hydrogenation of the furan concentrate is improvedand the capacity of the bed to hold the sulfur is increased by impregnating the zinc oxide with sodium hydroxide.

We claim: 1. A process for extending the life of hydrogenation catalysts and improving the hydrogenatability of furan concentrates to produce high purity tetrahydrofuran products which comprises contacting a furan concentrate containing deleterious unsaturated hydrocarbon contaminants and sulfur compounds. but which is sub stantially free of high boiling materials. prior to hydrogenation. with zinc oxide at a temperature ranging from about 550 to about 850F for a finite period of time sufficient to render innocuous compounds present in said concentrate which tend to inactivate hydrogenation catalysts, and hydrogenating said concentrate substantially free of catalyst inactivating materials by contacting with a hydrogenation catalyst and hydrogen under hydrogenation conditions sufficient to hydrogenate said unsaturated hydrocarbons to paraffinic materials and convert said concentrate substantially to a high purity tetrahydrofuran product.

2. A process according to claim 1 wherein said furan concentrate is separated into a fraction boiling above about "C and a fraction boiling below about 80C and further wherein the fraction boiling below about 80C is contacted with zinc oxide prior to hydrogenation.

3. A process according to claim 1 wherein the furan concentrate is contacted with zinc oxide and the effluent from the zinc oxide treatment separated into a fraction boiling above 80C and a fraction boiling below 80C with the further proviso that the fraction boiling below about 80C is then subjected to hydrogenation.

4. A process according to claim 1 wherein hydrogen is added to the furan concentrate prior to contacting with Zinc oxide.

5. A process according to claim 1 wherein said furan concentrate is subjected to distillation to remove overhead a fraction boiling below about 80C which fraction is then contacted with zinc oxide in the presence of added hydrogen prior to hydrogenation.

6. A process according to claim 1 wherein said furan concentrate is obtained from the effluent of an oxidative dehydrogenation process and the concentrate contains in addition oxygenated hydrocarbons as contaminants and is subjected to distillation to remove overhead materials boiling below about 80C and then contacted with zinc oxide in the presence of added hydrogen before being passed to hydrogenation.

7. A process according to claim 1 wherein said hydrogenation is carried out under temperature conditions of l00400F and in the presence of a cobalt, nickel or ruthenium catalyst effective for hydrogenating the unsaturated hydrocarbon materials present to paraffinic materials and to convert furan to tetrahydrofuran.

8. A process according to claim 1 wherein the zinc oxide has been treated with a base prior to contacting with the furan concentrate.

9. A process according to claim 8 wherein the base is sodium hydroxide and the amount of base added to the zinc oxide is in the range 1 to 10 weight percent. 

1. A PROCESS FOR EXTENDING THE LIFE OF HYDROGENATION CATALYLYSTS AND IMPROVING THE HYHYDROGENATABILITY OF FURAN CONCENTRATES TO PRODUCE HIGH PURITY TETRAHYDROFURAN PRODUCTS WHICH COMPRISES CONTACTING A FURAN CONCENTRATE CONTAINING DELETERIOUS UNSATURATED HYDROCARBON CONTAMINANTS AND SULFUR COMPOUNDS, BUT WHICH IS SUBSTANTIALLY FREE OF HIGH BOILING MATERIALS, PRIOR TO HYDROGENATION, WITH ZINC OXIDE AT A TEMPERATURE RANGING FROM ABOUT 550 TO ABOUT 850*F FOR A FINITE PEROID OF TIME SUFFICIENT TO RENDER INNOCUOUS COMPOUNDS PRESENT IN SAID CONCENTRATE WHICH TEND TO INACTIVATE HYDROGENATION CATALYSTS, AND HYDROGENATING SAID CONCENTRATE SUBSTANTIALLY FREE OF CATALYST INACTIVATING MATERIALS BY CONTACTING WITH A HYDROGENATION CATALYST AND HYDROGEN UNDER HYDROGENATION CONDITIONS SUFFICIENT TO HYDROGENATE SAID UNSATURATED HYDROCARBONS TO PARAFFINIC MATERIALS AND CONVERT SAID CONCENTRATE SUBSTANTIALLY TO A HIGH PURITY TETRAHYDROFURAN PRODUCT.
 2. A process according to claim 1 wherein said furan concentrate is separated into a fraction boiling above about 80*C and a fraction boiling below about 80*C and further wherein the fraction boiling below about 80*C is contacted with zinc oxide prior to hydrogenation.
 3. A process according to claim 1 wherein the furan concentrate is contacted with zinc oxide and the effluent from the zinc oxide treatment separated into a fraction boiling above 80*C and a fraction boiling below 80*C with the further proviso that the fraction boiling below about 80*C is then subjected to hydrogenation.
 4. A process according to claim 1 wherein hydrogen is added to the furan concentrate prior to contacting with zinc oxide.
 5. A process according to claim 1 wherein said furan concentrate is subjected to distillation to remove overhead a fraction boiling below about 80*C which fraction is then contacted with zinc oxide in the presence of added hydrogen prior to hydrogenation.
 6. A process according to claim 1 wherein said furan concentrate is obtained from the effluent of an oxidative dehydrogenation process and the concentrate contains in addition oxygenated hydrocarbons as contaminants and is subjected to distillation to remove overhead materials boiling below about 80*C and then contacted with zinc oxide in the presence of added hydrogen before being passed to hydrogenation.
 7. A process according to claim 1 wherein said hydrogenation is carried out under temperature conditions of 100*-400*F and in the presence of a cobalt, nickel or ruthenium catalyst effective for hydrogenating the unsaturated hydrocarbon materials present to paraffinic materials and to convert furan to tetrahydrofuran.
 8. A process according to claim 1 wherein the zinc oxide has been treated with a base prior to contacting with the furan concentrate.
 9. A process according to claim 8 wherein the base is sodium hydroxide and the amount of base added to the zinc oxide is in the range 1 to 10 weight percent. 